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Remote Sensing Glossary for Teachers and
Students
(Grades 6-12)
| A-D | E-G | H-M | N | O-Z | Bibliography |
Terms, Definitions and Concepts (E-G)
Electromagnetic radiation: Energy propagated as
time-varying electric and magnetic fields. These two fields are
inextricably linked as a single entity since time-varying electric fields
produce time-varying magnetic fields and vice versa. Light and radar are
examples of electromagnetic radiation differing only in their wavelengths
(or frequency). Electric and magnetic fields propagate through space at
the speed of light.
Electromagnetic
spectrum: The entire ranges of radiant energies or waves
frequencies from the longest to the shortest wavelengths--the
categorization of solar radiation. Satellite sensors collect this energy,
but what the detectors capture is only a small portion of the entire
electromagnetic spectrum. The spectrum usually is divided into seven
sections: radio, microwave, infrared, visible, ultraviolet, x-ray, and
gamma-ray radiation. See diagram below.
Landsat collects monochrome images in each band by measuring
radiance & reflectance in each channel. When viewed individually,
these images appear as shades of gray.
 The chart shows the various
TM bands and typical applications.
False color or false color composite image:
Used to interpret radiance measurements in infrared portion of the EM
spectrum, we assign colors to the bands of interest and then combine them
into a "false color" composite image. See digital image.
Near Infrared Composite (4,3,2) Adding a near infrared (NIR)
band and dropping the visible blue band creates a near infrared composite
image. Vegetation in the NIR band is highly reflective due to chlorophyll,
and an NIR composite vividly shows vegetation in various shades of red.
Water appears dark, almost black, due to the absorption of energy in the
visible red and NIR bands.
Shortwave Infrared Composite (7,4,3 or 7,4,2) A shortwave
infrared composite image is one that contains at least one shortwave
infrared (SWIR) band. Reflectance in the SWIR region is due primarily to
moisture content. SWIR bands are especially suited for camouflage
detection, change detection, disturbed soils, soil type, and vegetation
stress.
Geographic Information System (GIS): A system for
archiving, retrieving, and manipulating data that has been stored and
indexed according to the geographic coordinates of its elements. The
system generally can utilize a variety of data types, such as imagery,
maps. table, etc.
Geostationary: Describes an orbit in which a
satellite is always in the same position (appears stationary) with respect
to the rotating Earth. The satellite travels around the Earth in the same
direction, at an altitude of approximately 35,790 km (22,240 statute
miles) because that produces an orbital period equal to the period of
rotation of the Earth (actually 23 hours, 56 minutes, 04.09 seconds).
Global Change Research Program (GCRP) The USGCRP is a
government-wide program whose goal is "to establish a scientific basis for
national and international policy-making relating to natural and
human-induced changes in the global Earth system." The Global Change
Research Program coordinates and guides the efforts of federal agencies.
The program examines such questions as, is the Earth experiencing global
warming? Is the depletion of the ozone layer expanding? How do we
determine and understand the causes of global climate changes? Are they
reversible? What are the implications for human needs and activities?
Global Learning and Observations to Benefit the Environment
(GLOBE): is a worldwide network of students, teachers, and scientists
working together to study and understand the global environment. Students
and teachers from over 7,000 schools in more than 80 countries are working
with research scientists to learn more about our planet. http://globe.fsl.noaa.gov/
Grayscale: Environmental satellite scanners, rather
than photographing a scene, scan a scene line-by-line measuring light or
heat levels and transmitting this information as a video image via an
amplitude modulated (AM) sub carrier contained in the satellite's FM
signal. The video image--a 2400 Hz tone--is amplitude modulated to
correspond to the light and dark areas sensed, with the louder portion of
the tone representing the lighter areas of the image and the lower portion
of the tone representing the darker areas of the image. Intermediate
volumes form the shades of the gray scale (up to 256 shades) needed to
complete the image. This is an analog type of data transmission, and
enables the assessment of such features as heat, light, temperature, and
cloud heights.
Ground Validation: information collected at the same site that a
remote sensing system collects the data. Ground validation data are used
to interpret, accuracy access and calibrate remotely sensed
observations.
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